Classic markup-and-discount question — the kind that trips people up when there are successive discounts involved. Let's assign a cost price and work through each retailer.
Key concept being tested: Successive percentage changes (Percent and Interest Problems) — specifically, how successive discounts compound.
Let cost price = 100.
Step 1 — Retailer A: 50% markup → MP = 150. Then 40% discount on MP.
Selling price A = 150 × 0.60 = 90
Step 2 — Retailer B: 100% markup → MP = 200. Two successive 30% discounts.
After first discount: 200 × 0.70 = 140
After second discount: 140 × 0.70 = 98
Step 3 — Retailer C: 20% markup → MP = 120. 20% discount on MP.
Selling price C = 120 × 0.80 = 96
Step 4 — Order: B (98) > C (96) > A (90) → Answer: A (B > C > A)
Common trap: Students calculate B's double discount as a single 60% discount (thinking 30% + 30% = 60%), giving them 200 × 0.40 = 80. That's wrong — successive discounts are multiplicative, not additive. Two 30% discounts = 1 − (0.70 × 0.70) = 51% total discount, not 60%. This mistake flips B from the highest selling price to the lowest, completely reversing the order.
Also watch out for Retailer C — a 20% markup followed by a 20% discount does NOT get you back to cost price. You end up at 96, not 100. Equal markup and discount percentages are never a wash.
Answer: A (B > C > A)
Takeaway: Whenever you see successive discounts, always multiply the multipliers (0.70 × 0.70), never add the percentages — and remember that symmetrical markup and discount percentages will always result in a net loss, not a breakeven.